Bipolar electrosurgical instrument for sealing vessels

ABSTRACT

A bipolar electrosurgical instrument has opposable seal surfaces on its jaws for grasping and sealing vessels and vascular tissue. Inner and outer instrument members allow arcuate motion of the seal surfaces. An open lockbox provides a pivot with lateral support to maintain alignment of the lateral surfaces. Ratchets on the instrument members hold a constant closure force on the tissue during the seal process. A shank portion on each member is tuned to provide an appropriate spring force to hold the seal surfaces together. During surgery, the instrument can be used to grasp and clamp vascular tissue and apply bipolar electrosurgical current through the clamped tissue. In one embodiment, the seal surfaces are partially insulated to prevent a short circuit when the instrument jaws are closed together. In another embodiment, the seal surfaces are removably mounted on the jaws.

FIELD OF THE INVENTION

This invention relates to an electrosurgical instrument for permanentlyclosing vessels in a human or animal, and more particularly to a bipolarelectrosurgical instrument that seals vessels and vascular tissue byapplying a combination of pressure and electrosurgical current.

BACKGROUND OF THE DISCLOSURE

A hemostat is commonly used in surgical procedures to grasp, dissect andclamp tissue. It is typically a simple pliers-like tool that usesmechanical action between its jaws to constrict vessels without cuttingthem. It is also typical for hemostats to have an interlocking ratchetbetween the handles so that the device can be clamped and locked inplace.

Many hemostats are used in a typical open-surgical procedure. Oncevascular tissue has been clamped with a hemostat, it is common for asurgeon to tie a suture around the tissue to close it off permanentlyprior to removing the hemostat. Several hemostats may be left in thesurgical field until the surgeon has the opportunity to tie a suturearound each section of clamped tissue.

Small blood vessels have been closed using electrosurgical instrumentswithout the need for sutures. For example, neurosurgeons have usedbipolar instruments to coagulate vessels in the brain that are smallerthan two millimeters in diameter. These bipolar instruments aretypically tweezer-like devices with two arms that can be deflectedtoward each other to grasp tissue. However, it has been found that theseinstruments are not capable of sealing blood vessels with diameterslarger than about two millimeters. There has been a long-felt need foran easy way to seal larger vessels and vascular tissue bundles withoutthe need for sutures.

It is thought that the process of coagulating small vessels isfundamentally different than vessel sealing. Coagulation is defined as aprocess of desiccating tissue wherein the tissue cells are ruptured anddried. Vessel sealing is defined as the process of liquefying thecollagen in the tissue so that it crosslinks and reforms into a fusedmass. Thus, coagulation of small vessels is sufficient to permanentlyclose them. Larger vessels need to be sealed to assure permanentclosure.

A number of bipolar electrosurgical forceps and clamps are known in thefield. However, these instruments are not designed to apply the correctpressure to a blood vessel to achieve a lasting seal. All of theseinstrument also suffer from the drawback that they do not combine thesimplicity and familiarity of a hemostat with a bipolar electrosurgicalcircuit.

An example of a bipolar electrosurgical power curve for vessel sealingis disclosed in a U.S. patent application entitled, “Energy DeliverySystem for Vessel Sealing,” Ser. No. 08/530,495, filed Sept. 19, 1995,and is hereby incorporated by reference and made a part of thisdisclosure.

A U.S. patent application entitled, “Vascular Tissue Sealing PressureControl and Method,” Ser. No. 08/530,450, filed on Sep. 19, 1995,discloses another surgical tool for sealing vessels, and is herebyincorporated by reference and made a part of this disclosure.

U.S. Pat. No. 371,664 discloses a pair of electric forceps with positiveand negative electric poles located on the jaws.

U.S. Pat. No. 728,883 discloses an electrothemic instrument in whichelectricity is used to heat one of the jaws of the instrument.

U.S. Pat. No. 1,586,645 discloses a bipolar instrument for coagulatingtissue.

U.S. Pat. No. 2,002,594 discloses a bipolar laparoscopic instrument fortreating tissue, whereby coagulation and cutting of tissue can beperformed with the same instrument.

U.S. Pat. No. 2,176,479 discloses an instrument for finding and removingmetal particles. The jaws of the instrument are designed to complete anelectrical circuit when conductive material is placed therebetween. Aninsulated pivot and an insulated ratchet are used to prevent a shortcircuit.

U.S. Pat. No. 3,651,811 discloses a bipolar electrosurgical instrumentfor cutting and coagulating tissue.

U.S. Pat. No. 4,005,714 discloses bipolar coagulation forceps with jawsthat open and close by way of an actuating sleeve.

U.S. Pat. Nos. 4,370,980 and 5,116,332 disclose an electrocauteryhemostats wherein the hemostatic clamping function and theelectrocautery function may be accomplished with a single instrument.Monopolar electrosurgical designs are shown and described.

U.S. Pat. No. 4,552,143 discloses a family of removable switchelectrocautery instruments, including an electrocautery hemostat.Monopolar electrosurgical designs are shown and described.

U.S. Pat. No. 5,026,370 discloses an electrocautery forceps instrumenthaving an enclosed electrical switching mechanism. Monopolarelectrosurgical designs are shown and described.

U.S. Pat. No. 5,443,463 discloses coagulating forceps having a pluralityof electrodes.

U.S. Pat. No. 5,484,436 discloses bipolar electrosurgical instrumentsfor simultaneously cutting and coagulating tissue.

The article, “The Mechanism of Blood Vessel Closure by High FrequencyElectrocoagulation” discloses experiments upon the blood vessels ofdogs. The sentence starting on the last line of page 823 describes “anelectrode forceps, each of the blades being insulated form the other andeach connected to a terminal of the high frequency generator.”

The article, “Studies on coagulation and development bipolar coagulator”discloses on page 150 that, “It was not possible to coagulate safelyarteries with a diameter larger than 2 to 2.5 mm.” On page 151, line 5,it is noted that “Veins can be coagulated safely up to a diameter of 3to 4 mm.”

Russian Patent 401,367 discloses a bipolar instrument with a linkagethat brings the working jaws together in a parallel manner.

Prior disclosures have not provided a design for a bipolarelectrosurgical instrument capable of conveniently applying a constantpressure, from a calibrated spring-loaded source held by a ratchet, thatis sufficient to seal vessels and vascular tissue.

SUMMARY OF THE INVENTION

It is the general objective of this invention to provide a bipolarelectrosurgical instrument that can fuse tissue without the need for asuture or surgical clips. The instrument conducts electrosurgicalcurrent between two seal surfaces located on opposable jaws. Theelectrosurgical current passes through tissue clamped between the jawsand remolds the collagen to fuse the tissue and form a permanent seal.

One advantage of the invention is that blood vessels can be quicklyfused and permanently sealed against passage of blood or other fluids.The instrument thereby reduces operating-room time, provides improvedaccess to target tissues, and increases the efficiency of the surgicalprocedure.

Another advantage is that no sutures or staples are required topermanently seal blood vessels, and no foreign material is left in thebody of the patient.

Yet another advantage is that vessels can be sealed as the instrument isapplied, and then the instrument can be removed from the surgical field.This keeps the surgical field clear of extraneous tools that may hinderthe surgeon's access to the surgical site.

Yet another advantage is that the proper amount of pressure can beapplied by the instrument to the vessel or vessels, thereby increasingthe likelihood of a successful surgical outcome.

The bipolar electrosurgical instrument of the present inventioncomprises inner and outer members connected by an open lockbox,interlocking ratchet teeth, and electrical terminals with conductivepathways leading to seal surfaces. The inner and outer members each havea ring handle near a proximal end and an opposable seal surface near adistal end. The proximal end is held and controlled by the surgeon,while the distal end is used to manipulate tissue. The open lockboxjoins the inner and outer members to allow arcuate motion of eachopposable seal surface. The open lockbox is generally designed toprovide lateral support so that both seal surfaces move in approximatelythe same plane. The seal surfaces are preferably aligned opposite eachother when the instrument jaws are closed together. To provide lateralsupport, the open lockbox comprises a pivot and at least one flangeextending over the inner member and attached to the outer member.

The instrument is tuned to provide a proper closure force by adjustingthe dimensions of a shank portion on each of the inner and outermembers. The shank portion is defined as the portion of each memberbounded by its respective ratchet stub and the open lockbox. During use,the surgeon squeezes the ring handles to compress tissue between theseal surfaces. The shank portion of each member flexes in the manner ofa cantilever spring, and can be locked in a deflected position with theratchet to hold a constant force. It is one of the objects of theinvention to provide a range of ratchet stops that correspond to a rangeof appropriate closure forces on the seal surfaces of the instrument.

Ratchet teeth are located on each member near the ring handle. Theratchet teeth are generally designed to interlock against the springforce from the shanks. The spring force is thus transmitted through thepivot to hold the seal surfaces against each other. A range of closureforces is required in an instrument, depending on the type and thicknessof the tissue to be sealed. It is thus desirable to have several ratchetstops, each providing a progressively larger force to the seal surfaces.

An electrical connector is located on each ring handle. The electricalconnector may be a metal post that is integrally formed with the memberand ring handle. Bipolar electrical cables from an electrosurgicalgenerator are connected to the instrument at the electrical connectors.An electrically conductive path on each of the inner and outer membersconducts the electrosurgical current to the seal surfaces. Theelectrically conductive path may be along the stainless steel members.An electrically insulative coating is preferably bonded to the outersurfaces of the members to protect the surgeon and patient againstinadvertent electrical burns.

The following terms are herein defined as follows. The applied force ofthe instrument is the total force being applied to the tissue betweenthe jaws. The jaws are the members near the distal end of theinstrument, from the lockbox to the tip of the instrument. Theelectrodes are the metal surfaces that conduct electricity to thetissue. The seal surface is the feature on the electrode that comes indirect contact with the tissue. The shank is the portion of each memberbetween the lockbox and the ratchet. The ring handles are the elementson the members, near the proximal end of the instrument, that aregrasped by the surgeon. The lockbox is the structure that allows themembers to pivot, including the pivot pin and other cooperatingsurfaces. The inner member is the member that is generally captured inthe interior of the lockbox. The outer member is the member that is onthe outside of the lockbox. Electrode pressure is calculated by dividingthe applied force over the complete area of the seal surface. Tissuepressure is calculated by dividing the applied force over the area oftissue placed between the jaws.

It has been found through experimentation that an instrument for vesselfusion (also referred herein as vessel seing) should compress the tissuewith a proper amount of pressure between the instrument jaws. Thepressure is preferably sufficient to close any blood-carrying lumen. Thepressure is preferably low enough so that the tissue is not split apartwithin the instrument jaws.

The jaws of the instrument should not short-circuit during theprocedure. The tissue will typically decrease in thickness whenelectrosurgical current is applied, thereby allowing the seal surfacesto move closer together. This decrease in thickness should not result inthe electrodes making direct contact with each other. Otherwise, a shortcircuit could give the electrosurgical current a preferential patharound the tissue and may result in a poor seal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a bipolar instrument for vessel fusion,shown partially exploded.

FIG. 2 is a schematic plan view of a bipolar instrument for vesselfusion having a longer curved jaw.

FIG. 3 is a side view of the instrument shown in FIG. 2.

FIG. 4 is a schematic plan view of an alternative embodiment of aninstrument for vessel fusion having a shorter curved jaw.

FIG. 5 is side view of the instrument shown in FIG. 4.

FIG. 6 is a schematic plan view of an alternative embodiment of aninstrument for vessel fusion having a straight jaw.

FIG. 7 is a side view of the instrument shown in FIG. 7.

FIG. 8 is a perspective view of a shoulder pin.

FIG. 9 is a side view of a shoulder pin.

FIG. 10 is a front view of a shoulder pin.

FIG. 11 is a top view each of a pair of seal surfaces showing conductiveregions and insulative regions that prevent a short circuit when theseal surfaces are mated in opposition.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, the instrument 10 has an inner member 11 and anouter member 12. The members 11 and 12 are connected through an openlockbox 13 which has a gap between flanges 33. The terms “inner” and“outer” are used to distinguish the members 11 and 12, and theircomponent parts, according to the members' respective positions at theopen lockbox 13. The inner member 11 is fitted generally within theinner surfaces of the open lockbox 13 and is captured by the flanges 33.The outer member generally forms the outside surfaces of the openlockbox 13.

The inner member 11 has an inner shank 14, an inner jaw 16, and an innerring handle 20. Similarly, the outer member 12 has an outer shank 15, anouter jaw 17, and an outer ring handle 21. The ring handles, 20 and 21,are designed for a surgeon to hold and manipulate the instrument 10. Thejaws, 16 and 17, are designed to grasp tissue between the opposing sealsurfaces 18 and 19.

Each shank, 14 and 15, has a respective ratchet stub 24 or 25. Ratchetteeth, 26 and 27, are designed to interlock in a manner that hold themembers, 11 and 12, in position. The shanks 14 and 15 are deflected inthe manner of a cantilever spring when the jaws are forced together bythe surgeon. The deflection of the shanks 14 and 15 produces a springrestoring force that can be opposed by interlocking the ratchet teeth,26 and 27.

The instrument 10 does not cause a short circuit when the ratchet teeth,26 and 27, are interlocked. This is accomplished by a suitable selectionand placement of electrically insulating materials. In the preferredembodiment, the ratchet teeth 26 and 27 are composed of a polymericmaterial which is press-fit into the ratchet stubs 24 and 25. A ratchetscrew 28 is used in the preferred embodiment to secure the ratchet teeth26 and 27 into the ratchet stubs 24 and 25. During manufacture, theratchet teeth 26 and 27 may be formed from a blank after the blank hasbeen press fit into the ratchet stubs 24 and 25.

In a second embodiment, one of the members, 11 or 12, includes theratchet stub and ratchet teeth as in integral part of the member, whilethe other member, 12 or 11, has an insulative layer that prevents ashort circuit between the members 11 and 12 when the ratchets areengaged.

The open lockbox 13 has the function of providing a pivoting joint forthe members 11 and 12. In addition, the flanges 33 provide lateralsupport to help maintain alignment of the jaws 16 and 17. Closed lockboxdesigns are typically used in standard hemostat designs, wherein aninner member is completely captured through a slot in an outer member.The open lockbox 13 in present invention has a gap between the flanges33 that is different from a closed lockbox design. The gap in the openlockbox 13 provides convenient access to install an electricallyinsulated pivot.

The electrically insulated pivot in the present invention comprises ashoulder washer 29 supporting a lockbox screw 30. The shoulder washer 29is composed of an electrically insulative material that prevents a shortcircuit between the members 11 and 12. A large screw cap 31 fits overthe head of the lockbox screw 30. A small screw cap 32 fits over thethreaded end of the lockbox screw 30.

Each member 11 and 12 is connected to a pole of a bipolarelectrosurgical generator. Electrical connectors 22 and 23 are locatedon the ring handles 20 and 21 to provide a convenient point ofconnection. The members 11 and 12 are formed of an electricallyconductive material, such as stainless steel. The exposed surfaces ofthe members, except for the connectors 22 and 23 and the seal surfaces18 and 19, are preferably spray coated with an insulating material.

The characteristics of the bipolar electrosurgical current aredetermined by the design of the electrosurgical generator. In thepreferred embodiment, the generator will have an output wherein thepeak-to-peak voltage will not exceed 130 Volts. This is because highervoltages can cause sparking which results in localized burning of tissuewhich may result in a failure of the tissue weld. The preferredembodiment has the generator capable of producing high frequency outputcurrent of at least 2 Amps RMS. High electrical current is importantbecause it heats the tissue sufficiently to melt the collagen. Lowerelectrical currents will often produce weak tissue welds with lowbursting strength.

During operation, the instrument 10 is used to grasp tissue between theseal surfaces 18 and 19. The surgeon squeezes the ring handles 20 and 21together, causing pressure to be applied to the tissue. The ratchetteeth 26 and 27 are interlocked at the appropriate ratchet setting,depending on the tissue type and tissue thickness. Bipolarelectrosurgical current is applied through the instrument and the tissueto cause the tissue to fuse.

The jaws 16 and 17 have a structure and cross-section that resistbending under load. Thus, for purposes of engineering analysis, theshank portions 14 and 15 act as a cantilever supported beam once theseal surfaces 18 and 19 have been mated. The length of this idealizedcantilever beam extends from the lockbox screw 30 to the location of therespective ratchet subs 24 or 25. It is possible to model each shank asa cantilever spring having a spring constant. Each ratchet position isdesigned to transmit a particular closure force to the jaws 16 and 17against the action of the restoring force of the cantilever spring.

The spring constant is generally a function of Young's Modulus of theshank material, the moment of inertia of the shank, and the length ofthe shank portion 14 and 15. When the jaws 16 and 17 of the instrument10 are closed together, each shank 14 and 15 approximates acantilever-supported beam. It is properly assumed that the deflection ofeach shank 14 and 15 remains within the linear range of itsstress-strain curve. The behavior of such a beam is well known tomaterials engineers. A large spring constant will result in largeclosure forces between the seal surfaces 18 and 19. Similarly, a smallspring constant will result in a small closure forces between the sealsurfaces 18 and 19. The choice of a proper spring constant will dependon the length of the shank 14 or 15 and the distance between ratchetstops 26 and 27.

Experimental results in animal studies suggest that the magnitude ofpressure exerted on the tissue by the seal surfaces 18 and 19 isimportant in assuring a proper surgical outcome. Tissue pressures withina working range of 7 kg/cm² to 13 kg/cm² have been shown to be effectivefor sealing arteries and vascular bundles. It is desirable to tune thespring constant of the shank portions 14 and 15, in conjunction with theplacement of the ratchet teeth 26 and 27, such that successive ratchetpositions will yield pressures within the working range. In oneembodiment, the successive ratchet positions are two millimeters apart.

Pressure on the tissue can be described in several ways. Engineers willrecognize that the amount of pressure exerted on the tissue depends onthe surface area of the tissue that is in contact with the sealsurfaces. In the one embodiment, the width of each seal surface 18 and19 is in the range of 2 to 5 millimeters, and preferably 4 millimeterswidth, while the length of each seal surface 18 and 19 is preferably inthe range of 10 to 30 millimeters. It has been found throughexperimentation that at least one interlocking ratchet positionpreferably holds the closure force between approximately 400 and 650grams per millimeter of seal surface width. For example, if the width ofthe seal surface 18 and 19 is 4 millimeters, the closure force ispreferably in the range of 1600 grams to 2600 grams. In one embodiment,the closure force is 525 grams per millimeter of width, yielding aclosure force of 2100 grams for a 4 millimeter width seal surface 18 and19.

It has been found experimentally that local current concentrations canresult in an uneven tissue effect, and to reduce the possibility of thisoutcome, each seal surface 18 and 19 has a radiused edge in thepreferred embodiment. In addition, a tapered seal surface 18 and 19 hasbeen shown to be advantageous in certain embodiments because the taperallows for a relatively constant pressure on the tissue along the lengthof the seal surfaces 18 and 19. The width of the seal surfaces 18 and 19is adjusted, in certain embodiments, wherein the closure force dividedby the width is approximately constant along the length.

In one embodiment, a stop 37, made from insulative material, is locatedin the instrument to maintain a minimum separation of at least 0.3millimeters between the seal surfaces 18 and 19, as shown in FIG. 1. Thestop 37 reduces the possibility of short circuits between the sealsurfaces 18 and 19.

In certain embodiments, as shown in FIG. 11, the seal surfaces 18 and 19comprise conductive regions 38 and insulative regions 39 arranged suchthat each conductive region 38 opposes an insulative region 39 when theopposable seal surfaces 18 and 19 are mated in opposition. The sealsurfaces 18 and 19, in certain embodiments, may be removable from itsrespective member 11 or 12 by standard mechanical interfaces, such as apin and socket arrangement.

FIG. 2 shows an embodiment for a thirty-two millimeter curved sealsurface. FIG. is a side view of FIG. 2. The members 11 and 12 in FIG. 2are formed from, American Iron and Steel Institute 410 stainless steel.The length and cross sectional area of the shank portions 14 and 15 areshown in FIGS. 2 and 3 to provide a spring constant of twenty-fivepounds per inch deflection.

The embodiment shown in FIGS. 4 and 5 has a twenty millimeter curvedseal surface. The embodiment shown in FIGS. 6 and 7 has a thirty-twomillimeter straight seal surface. Each embodiment in FIGS. 2 through 7is designed to have the look and feel of a standard hemostat.

FIGS. 8, 9 and 10 show three views of a shoulder pin 34 that can beused, in certain embodiments, instead of the lockbox screw 30 to connectthe members 11 and 12. The shoulder pin 34 has at least one ramp surface35 that engages one of the members 11 or 12 to cause increasingmechanical interference as the jaws 16 and 17 move toward each other. Inone embodiment, the shoulder pin 34 forms part of the open lockbox 13 toaid alignment of the seal surfaces 18 and 19. In another embodiment, theshoulder pin 34 is used without an open-lockbox 13, and movably pins themembers 11 and 12 together without a flange 33. The interference fit mayrequire the calibration of the instrument 10 to insure that the appliedforce will be sufficient to provide the appropriate working pressurebetween the seal surfaces 18 and 19. A slightly higher spring constantin the shank portions 14 and 15 is preferably used, depending on thelevel of interference caused by the shoulder pin.

A method of using the bipolar electrosurgical instrument comprises thefollowing steps. A surgeon grasps the ring handles 20 and 21 on theinstrument 10 to manipulate the jaws 16 and 17. A vessel or vasculartissue is compressed between the opposable seal surfaces 18 and 19. Theopposable seal surfaces 18 and 19 preferably come together in alignedopposition due to the alignment action of the open-lockbox 13, or incertain embodiments due to the alignment action of the shoulder pin 34.The surgeon further deflects the shank portions 14 and 15 of the members11 and 12 to engage the ratchet teeth 26 and 27. The engagement of theratchet teeth 26 and 27 hold the shank portions 14 and 15 in theirdeflected positions to provide a constant spring force that istransmitted as a closure force to the jaws 16 and 17. An electrosurgicalgenerator is connected to the instrument 10 through connectors 22 and 23on the ring handles 20 and 21. An electrical switch is used to close acircuit between the generator and the instrument 10. The switch may be afootswitch such as Valleylab's catalog number E6009, available fromValleylab Inc., Boulder Colo. The electrosurgical current flows throughan electrically conductive path on each of the inner and outer members11 and 12 between its respective electrical connector, 22 or 23, and itsrespective seal surface, 18 or 19. An electrically insulative coating 36substantially covers each member 11 and 12, except for the seal surfaces18 and 19, to protect the surgeon against electrical arcs.

It is to be understood that the above described embodiments are onlyillustrative of the application of the principles of the presentinvention. Numerous modifications and alternative arrangements may bedevised by those skilled in the art without departing from the spiritand scope of the present invention. The appended claims are intended tocover such modifications and arrangements.

What is claimed is:
 1. A method of using a bipolar electrosurgicalinstrument, the method comprising the following steps: moving inner andouter members to grasp tissue between opposable seal surfaces, the innerand outer members each having a ring handle near a proximal end and anopposable seal surface near a distal end; aligning the opposable sealsurfaces in opposition using an open lockbox, the open lockbox joiningthe inner and outer members to allow arcuate motion of each opposableseal surface, the open lockbox comprising a pivot and at least oneflange extending over the inner member and attached to the outer member;engaging ratchet teeth located near each ring handle, the ratchet teethproviding at least one interlocking ratchet position that holds aclosure force between the opposable seal surfaces; deflecting a shankportion on each of the inner and outer members to create a spring load,the shank portion bounded by its respective ratchet teeth and the pivot;connecting bipolar electrosurgical current to the instrument through anelectrical connector located on each ring handle, such that the currentflows through an electrically conductive path on each of the inner andouter members between its respective electrical connector and itsrespective seal surface to provide for electrosurgical current flowbetween the opposable seal surfaces, and wherein an electricallyinsulative coating substantially covers each ring handle, each shankportion, and the open lockbox.
 2. A bipolar electrosurgical instrumentcomprising: inner and outer members each including a distal end havingan opposable seal surface disposed thereon; one of the members having anopen lockbox sufficiently dimensioned to at least partially receive theother of the members; a pivot joining the inner and outer members andfor allowing motion of each opposable seal surface relative to eachanother; a ratchet disposed on one of said members having at least onecomplimentary interlocking ratchet disposed on the other of said membersfor holding a closure force between the opposable seal surfaces; and astop disposed on one of the opposable seal surfaces for maintaining aminimum separation distance between the opposable seal surfaces.
 3. Abipolar electrosurgical instrument according to claim 2 wherein saidstop is made from an insulative material.
 4. A bipolar electrosurgicalinstrument according to claim 2 wherein said pivot is made from aninsulative material.
 5. A bipolar electrosurgical instrument accordingto claim 2 wherein said pivot includes a shoulder pin having a rampsurface for varying the interference fit between the inner and outermembers during arcuate motion of each opposable seal surface.
 6. Abipolar electrosurgical instrument according to claim 2 wherein saidopposable seal surfaces are removable from said distal ends of saidinner and outer members.
 7. A bipolar electrosurgical instrumentaccording to claim 2 wherein said ratchet includes ratchet teeth whichare removably engageable with said ratchet.
 8. A bipolar electrosurgicalinstrument according to claim 7 wherein said ratchet teeth are made froman polymeric material.
 9. A bipolar electrosurgical instrument accordingto claim 7 wherein said ratchet teeth engage said ratchet in a press-fitmanner.
 10. A bipolar electrosurgical instrument comprising: inner andouter members each including a distal end having an opposable sealsurface disposed thereon; a shoulder pin made from an insulativematerial for joining the inner and outer members and for allowing motionof each opposable seal surface relative to each another, the shoulderpin having a ramp surface for varying the interference fit between theinner and outer members during relative motion of each opposable sealsurface; a ratchet disposed on one of said members having at least onecomplimentary interlocking ratchet disposed on the other of said membersfor holding a closure force between the opposable seal surfaces; and astop disposed on one of the opposable seal surfaces for maintaining aminimum separation distance between the opposable seal surfaces.
 11. Abipolar electrosurgical instrument according to claim 10 wherein saidstop is made from an insulative material.
 12. A bipolar electrosurgicalinstrument according to claim 10 wherein said opposable seal surfacesare removable from said distal ends of said inner and outer members.